1. Field of the Invention
This invention pertains generally to the field of display units provide flight traffic information to the pilot or flight crew of an aircraft.
2. Description of the Related Art
Conventionally, avionics engineers and aviation governing authorities are improving and providing pilots and flight crews with information necessary to identify in-flight traffic. One approach that has been taken is to provide the flight crew with information on the location of other aircraft in the area. One exemplary system, which is capable of providing this information, is known as traffic alert and collision avoidance system (“TCAS”). The system is required for many aircraft including those operated by airliners operating in the United States. The TCAS has been designed to interrogate transponders of other aircraft, sometimes referred to as intruder or target aircraft. The TCAS evaluates the threat of a collision with other targets and provides traffic advisories (“TAs”) and resolution advisories (“RAs”). A TA is presented to a pilot in situations in which the TCAS identifies other traffic in the area which may become a threat to the aircraft in a short period of time, and an RA is presented to the pilot when there is imminent threat to the aircraft of a collision. The RA can provide commands to the pilot corresponding to a collision avoidance maneuver.
Recently, a traffic information system referred to as automatic dependent surveillance broadcast (“ADS-B”) has evolved. The ADS-B system is capable of broadcasting position, velocity, and status information from an aircraft at regular intervals using position information obtained from onboard navigation systems. The ADS-B system may use a mode S transponder or other transmitter, and provide transmissions at regular intervals. As such, ADS-B transmitters need not be interrogated by another aircraft.
Another type of traffic information system is a traffic information services broadcast (“TIS-B”) system. The TIS-B system is typically a ground station which provides position, velocity, and status information of air and ground vehicles using information obtained from ADS-B, primary surveillance radar, secondary surveillance radar, and other systems. The TIS-B ground station provides a squitter message on a periodic basis similar to the squitter message in the ADS-B system. As such, the ADS-B system is commonly seen as an air-to-air link, and the TIS-B is seen as a ground-to-air link. Each of the systems provides a data link to another aircraft. A further source of traffic information may be provided from air traffic control (“ATC”) via looking out the window or through a ground based or other radar system. Such information can then be communicated by the ATC to any aircraft within the vicinity of the airport.
With a variety of systems available to provide traffic information to the pilot, there is the opportunity to receive traffic information from more than one source; if so, then a correlation algorithm may be applied to determine whether targets provided from one traffic system correlate with targets provided from a second traffic system. For uncorrelated traffic, a choice may be provided by using a traffic source selection method such as the one disclosed by Carrico in U.S. Pat. No. 7,148,816. In addition, a pilot operating an aircraft located on the ground tends to use a narrow display range which provides for better surface traffic information and improves his or her ground situational awareness. Although this surface traffic information is useful, the lack of additional useful information about off-screen traffic comprised of aircraft approaching to land or landing on a runway, taking-off from the runway, and/or operating a missed approach of the runway limits the pilot's situational awareness of nearby traffic approaching the airport. In addition, with an expected increase of airborne traffic in the foreseeable future, the chance of cluttering the information presented on the display unit may possibly increase, thereby possibly interfering with the pilot's efficient access to more applicable information.